The paper reconstructs John Locke’s critique of Edward Herbert’s conception of common notions presented in the Essay Concerning Human Understanding (1690). Though aimed at the epistemological significance of the term, the critique seems to miss the point, since due to the Platonic character of Herbert’s philosophy, the notions have also a metaphysical and religious significance overlooked by Locke. Thus the attack is justified only in part: for Herbert, the rationality of nature is understood as an ideal and not as a certain historic state of affairs, as Locke seems to suggest. It is an interesting feature of the discussion, that both the common notions and their critique is aimed at justification of religious rationality. The difference between both philosophers seems to have its roots in different understanding of knowledge. For Herbert it relates to an ideal, conceptual structure of reality, whereas for Locke it culminates in natural histories of cumulative character.